Open stock flowbox system

ABSTRACT

THIS INVENTION RELATES TO AN OPEN STOCK FLOWBOX SYSTEM FOR A PAPER OR BOARD MAKING MACHINE IN WHICH THE SYSTEM EMPLOYS AN ENCLOSED TANK WITH AN OPEN-TOP STAND PIPE IN A RECIRCULATION ARRANGEMENT FOR RECYCLING EXCESS STOCK FROM THE FULL ENCLOSED TANK, THERE BEING NO STOCK/AIR INTERFACE PRIOR TO THE SLICE SUCH THAT CRUST FORMATION AND WEB BREAKAGE IS AVOIDED.

July 3, 1973 a. w. ATTWOOD E'TAL 3,743,573

OPEN s'rocx FLOWBOX SYSTEM Original Filed May 29, 1969 2 Sheets-Shet 1 July 3, 1973 w. ATTWOOD ETAL 3,743,573

OPEN STOCK FLOWBOX SYSTEM Original Filed May 29, 1969 2 Sheets-Sheet 2 NZ R United States Patent Oifice 3,743,573 Patented July 3, 1973 3,743,573 OPEN STOCK FLOWBOX SYSTEM Brian William Attwood, Hanham, near Bristol, and

Harold George Curry, Hambrook, near Bristol, England, assignors to St. Annes Board Mill Company Limited Continuation of abandoned application Ser. No. 828,949, pg g, 1969. This application Oct. 4, 1971, Ser. No.

9 Claims priority, application Great Britain, July 4, 1968, 31,975/ 68 Int. Cl. D2115 1/06 U.S. Cl. 162-336 4 Claims ABSTRACT OF TIE DISCLOSURE This invention relates to an open stock flowbox system for a paper or board making machine in which the system employs an enclosed tank with an open-top stand pipe in a recirculation arrangement for recycling excess stock from the full enclosed tank, there being no stock/ air interface prior to the slice such that crust formation and web breakage is avoided.

This is a continuation of application Ser. No. 828,949 filed May 29, 1969, now abandoned.

This invention concerns a flowbox system for a paper or board making machine.

According to the present invention there is provided a flowbox system for a paper or board making machine comprising an enclosed tank, a stock inlet to the tank, a pump for feeding stock to the inlet, a stock outlet from the tank to the flowbox slice and a header tank communicating with said stock tank to receive overflow stock therefrom, said header tank being in communication with the pump inlet for recirculating excess stock therethrough.

With such an arrangement, the stock tank is maintained full. With no stock/air interface, no crusts form on the stock, and thus there is no risk of such crusts breaking away, flowing through the slice and spoiling the web or sheet being made. Such risks are run with flowboxes having open or pressured tanks even when sprays are employed. In the present case, crusts forming on the header tank stock cannot interfere with slice flow since such crust formation can only flow to the pump for distribution and recirculation and thus can be filtered before reaching the slice. Also, the present system provides, in the header tank, a reservoir of stock which dissipates any pressure pulsations arising in the stock.

Preferably the header tank extends above said stock tank and is open to the atmosphere. The header tank may include water sprays adapted to spray the open surface of the stock in said header tank.

Alternatively the header tank may be pressurised.

Preferably there are a plurality of adjustable overflow ports emerging from the upper wall of the stock tank and connecting with a manifold for withdrawing the stock from the stock tank and leading it to the header tank.

In a preferred embodiment the stock is fed to the stock tank from an inlet distributor pipe which forms part of a stock recirculation system. Thus the feed distributor pipe and header tank return pipes may form part of a common recirculation system.

' In one embodiment the stock feed from tank to slice is through a plurality of shear tubes. The tubes may be arranged at acute angles one to the other to prevent streaking of the stock at the slice.

The invention is illustrated merely by day of example in the accompanying drawings in which:

FIG. 1 is a diagrammatic elevation of a flowbox system according to the present invention,

FIG. 2 is a plan of the system of FIG. 1 and FIG. 3 is an end elevation of the system of FIG. 1.

Referring to the drawings the flowbox system illustrated comprises an enclosed stock tank 10 to which stock is fed from a tapered inlet distributor pipe 11 through a plurality of transversely spaced pipes 12. The stock within the tank 10 passes through a plurality of transversely spaced shear tubes 13 into an explosion chamber 14 and thus to an adjustable slice 15 from which the stock emerges as a jet onto the machine wire (not shown) for dewatering to form a web of paper or board. The particular explosion chamber and shear tube arrangement is disclosed in more detail in our co-pending U.S. application No. 656,263 (now U.S. Pat. No. 3,565,758).

As seen clearly in FIGS. 1 and 2 the shear tubes '13 are disposed at acute angles one to the other to prevent streaking of the stock within the explosion chamber 14 and slice 15. Screws 19 are disposed at intervals across the slice 15 to provide, through rods 20*, a means for adjusting the size of the slice.

Stock at say, 3% consistency is fed from a constantly replenished reservoir 20a, via a line 21 containing a valve 22 to a pump 23. Make-up (or white) water from a constantly-replenished reservoir (and catch tank) 29 is added to the stock to reduce its consistency to say, 1.5%. The diluted stock is pumped by pump 23 through a strainer 24, flow meter 25 and valve 26 to the tapered inlet pipe 11.

The stock passing through pipe 11 and not entering tank 10 flows via a return tube 30 including a valve 27 to an open top header tank 31. The lower end of tank 31 is connected to the inlet side of pump 23 by a return pipe 32 containing a valve 33 and a flow meter 34.

Connected to the roof or uppermost wall of the tank 10 are a plurality of individually adjustable overflow pipes 42 spaced across the flowbox and connected to a common overflow pipe or manifold 43 which in turn communicates with the header tank 31. Each pipe 42 is provided with a valve 49.

Tank 31 extends above tank 10 and is open to atmosphere, and a water spray 35 is disposed in the open top end to play onto the water surface in the tank and prevent or minimise crust formation. To provide a visual indication of the head of stock in the tank 31, the wall of the tank may be made of transparent material.

The various valves provided (e.g. 22, 26, 27, 33 and 49) are adjusted to ensure a complete and regular flow of stock through pipe 11, with a regular flow through slice 15. The stock jet of velocity at slice 15 can be determined from the difference in readings of flow meters 25 and 34 and the size of slice 15.

The valves 49 on pipes 42 are adjusted such that tank 10 is maintained at capacity. Thus stock continually flows out of tank 10 through pipes 42 to header tank 31 and is recirculated to pump 23. The supply to pipe 11 must exceed the amount of stock flowing out through the slice 15 and the amount flowing through overflow pipes 42, the diflerence being returned to pump 23 via return pipe 30.

By maintaining the tank 10 at capacity, there is no stock/air interface, crusts which normally form on the open surface of the stock are eliminated and thus the stock is kept clean. Furthermore, pulsations are substantially reduced due to the body of stock in tank 31 and thus the profile of the sheet is improved. Also, aeration of the stock is reduced since the air/ stock surface area is reduced.

The only stock/air interface is that provided in tank 31. Since this is a vertical pipe of small surface area of stock, any crust formation is small. Also, any breakaway of such crusts will not reach the slice as they would from tank 10 but rather flow via pipe 32 to the pump 3-1 for redistribution and filtering. Thus breakages in the web caused by crusts formation are virtually avoided.

Although the system described above has included an open top box (through the header tank 31) it is clearly possible for the system to be completely pressurised with the same advantages being obtained. Thus tank 31 can be pressurised. Since the same surface area is involved, and tank 31 is not in flow communication with slice 15 directly the same advantages are obtained as with the open top system described above.

A similar system of maintaining a full flowbox can of course be used with alternative forms of slice outlet, the explosion chamber 14 fed by shear tubes 13 being one example only of the type of outlet suitable for this system.

Thus it is seen that trouble through crust formation (and to some extent pressure pulsations and aeration) can be reduced substantially by employing a header tank as described herein, the tank not being in direct flow communication with the slice. Furthermore present formation can be reduced by minimising the surface area of the tank e.g. by using a pipe such as 3-1.

A system such as that described above has been used with substantial success. Not only have breakages and poor web formation due to crust formation, pulsations and aeration been reduced considerably, but also maintenance has been reduced in view of the cleaner flowbox resulting from the development.

What we claim is:

1. An open stock feed system for a paper or board making machine comprising an enclosed tank, stock inlet means connected to the tank, a pump connected to said stock inlet means for feeding stock thereto, a slice, means connecting said tank to said slice for stock passage thereto, a return pipe connected to the stock inlet means for recirculating excess stock to the inlet side of the pump, a plurality of overflow ports disposed across the uppermost wall of the enclosed tank and connected to the inlet side of the pump by the return pipe and a header tank connected to the return pipe and to the overflow ports through a manifold, the header tank situated above the uppermost wall of the enclosed tank and providing a head of stock in the system and maintaining the enclosed tank full of stock.

2. An open stock feed system as claimed in claim 1 wherein a straining device is situated between the pump and the stock inlet of the enclosed tank to strain the stock fed to said stock inlet.

3. An open stock feed system as claimed in claim 1 provided with a distributor pipe communicating with a plurality of inlet ports in said enclosed tank for feeding stock thereto.

4. An open stock feed system as claimed in claim 3' including water sprays disposed in the open top end of the header tank for spraying the open surface of the stock in said header tank.

References Cited UNITED STATES PATENTS 3,351,522 11/1967 Lopas 162-337 2,688,276 9/ 1954- Showers 162-343 3,266,974 8/1966 Staver 162-2-l6 FOREIGN PATENTS 784,883 10/ 1957" Great Britain. 603,744 8/1960 Canada.

S. LEON BASHORE, Primary Examiner R. V. FISHER, Assistant Examiner U.S. Cl. X.R. 1623 39 

